She calls herself food babe. An activist blogger blowing the whistle on the bread used by a major food chain. She says it's dangerous no matter how you slice it. Subway, eat fresh. Reporter: The world's largest restaurant chain. Endorsed by athletes and the first lady. For years, subway has been providing meals that are healthy. Reporter: Is not under scrutiny. After their food was questioned by food blog activist von hari. Calling for the end of azodiacarbonamide. Mm. As soon as I heard there Michelle owe bah Marx the announcement that she is endorsing subway for children, I had to get involved. They use it because it makes the bread whiter and puffier. Reporter: It is usda and fda approved, but it's banned if other countries. Studies suggest it may increase the risk of asthma, and allergies before the petition, subway says they already decided to remove the ingredient from bread. Pending further approvals, we should finish the process in the coming weeks. I have a laundry list of companies doing this. I would like to see them all change. Yellow number 5. Reporter: She says she's successfully taken on large corporations like Kraft for dies used in their Mac and cheese. She's hoping this latest petition brings an increased awareness to what we eat. For "Good morning America," linsey Davis, ABC news, new York. And now we're back with our

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